1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device having a pad including a first pad portion, a second pad portion, and a bent pad portion, the first pad portion being misaligned with the second pad portion, for making a uniform contact area and for maintaining a uniform output voltage even when misalignment occurs due to heat expansion.
2. Discussion of the Related Art
The vast development of information also increases the demands for the development of display devices. Recently, many efforts have been made to study and develop various types of flat display panels, such as liquid crystal display devices (LCDs), plasma display panels (PDPs), electroluminescent displays (ELDs), and vacuum fluorescent displays (VFDs). Some of these types of flat display panels have been applied in and incorporated into a range of devices. For instance, LCDs have been commonly used as substitutions for cathode ray tubes (CRTs) in mobile image displays because of their high quality image, lightness, small thickness, compact size, and low power consumption. Although attempts have been made to incorporate LCDs into image devices for receiving broadcasting signals, such as televisions, and computer monitors. However, LCDs have not been as successfully incorporated into these image devices because the image quality has not been fully satisfactory. In order to implement a liquid crystal display device as a general display device, LCD development is dependent on realizing high image quality, high resolution, high brightness, and wide screen, while maintaining lightness, thin compactness, and low power consumption.
In general, a liquid crystal display device includes a liquid crystal panel for displaying an image and a driving unit for applying a driving signal to the liquid crystal panel. The liquid crystal panel includes first and second glass substrates bonded to each other with a predetermined space therebetween, and a liquid crystal material layer formed between the first and second glass substrates. The first glass substrate is commonly referred to as a thin film transistor (TFT) array substrate having a plurality of gate lines arranged along one direction at a predetermined interval from each other, a plurality of data lines arranged along a direction perpendicular to the gate lines at a predetermined interval from each other, a plurality of pixel electrodes formed in a matrix-arrangement within pixel areas defined by the gate and data lines crossing with each other, and a plurality of thin film transistors switched by signals of the gate lines to transfer signals of the data lines to the pixel electrodes. The second substrate is commonly referred to as a color filter substrate having a black matrix layer for cutting off light from a portion except in the pixel areas, an R/G/B color filter material layer for producing colored light, and a common electrode for producing an image. Spacers are used to separate the first and second substrates from each other with the predetermined space therebetween, and a sealant is used to bond the first and second substrates to each other.
The liquid crystal material layer may be formed in the liquid crystal panel by employing a liquid crystal injection process or a liquid crystal dropping process. The liquid crystal injection process includes coating a sealant on one substrate to form an injection inlet, bonding the substrate to a second substrate in a vacuum environment, and injecting liquid crystals therein through the injection inlet. The liquid crystal dropping process includes dropping liquid crystals on one substrate before bonding the two substrates to each other, and bonding a second substrate to the one substrate in a vacuum environment. Consequently, the driving unit is connected to the liquid crystal panel through a module mounting process. The module mounting process includes cleaning the liquid crystal panel, attaching a polarizing plate to the liquid crystal panel, and mounting a driving IC thereon. The diving IC generally is a tape carrier package (TCP) having tape automated bonding (TAB) integrated circuit (IC). An anisotropic conductive film (ACF) is first attached to a pad of the liquid crystal panel. While the TCP is aligned over the ACF, the TCP is bonded thereto by a pressurizing process. Bubbles generated from the pressurizing process (i.e, from a polarizing plate) are then removed. Thereafter, a TAB inspection, a resin coating process, a TAB attachment process, a welding process, an adjustment/test process, an assembly process, an aging process, and a final inspection are sequentially performed. Consequently, the TAB IC is connected directly to the liquid crystal panel to carry out signal and power supply on the TAB IC in accordance with a printed circuit board (PCB). Since the TAB IC is directly mounted on the liquid crystal panel, a thin LCD module can be mounted thereon, where a TCP output pad is connected to gate and data output pads of the liquid crystal panel using the ACF on the panel.
FIG. 1 illustrates a layout of a general liquid crystal display device, FIG. 2A illustrates a cross-sectional view of a general TAB package, and FIG. 2B illustrates an aligning layout of a liquid crystal panel pad and a TCP output pad according to a related art.
In FIG. 1, a first substrate 100, functioning as a thin film transistor array substrate and a second substrate 150, functioning as a color filter array substrate, are bonded to each other to form a liquid crystal panel having an active area 120. The first substrate 100 has a plurality of gate lines arranged along one direction at a predetermined interval from each other, a plurality of data lines arranged along a direction perpendicular to the gate lines at a predetermined interval from each other, a plurality of pixel electrodes formed in a matrix-arrangement within pixel areas defined by the gate and data lines crossing with each other, and a plurality of thin film transistors switched by signals of the gate lines to transfer signals of the data lines to the pixel electrodes. The gate and data lines have pads to connect a driving unit thereto. The second substrate 150 has a black matrix layer for cutting off light from a portion except the pixel areas, an R/G/B color filter material layer for producing colored light, and a common electrode for producing an image. Moreover, TCPs having driving ICs are bonded to the pads of the liquid crystal panel. For example, one TCP 101 having a gate driving IC 101a is connected to a printed circuit board 105, and the other TCP 102 having a data driving IC 102a is connected to another printed circuit board 106. The TCPs 101 and 102 are bonded to the gate and data pads 103 and 104 of the liquid crystal panel, respectively. Consequently, the gate driving IC 101a supplies the gate line with a driving voltage to sequentially turn ON/OFF the corresponding thin film transistor. The data driving IC 102a supplies the data line with a signal voltage to transfer a data voltage (i.e., video signal voltage) to the corresponding liquid crystal cell through the turned-ON thin film transistor.
In FIG. 2A, an anisotropic conductive film 115 is employed as a bonding material. The anisotropic conductive film 115 is coated on a pad area of the first substrate 100 of the liquid crystal panel 200. Polarizing plates 100a and 150a may be attached to the first and second substrates 100 and 150. Consequently, the TCP 101 or 102 having an output pad is aligned with the pads of the liquid crystal panel by placing over the anisotropic film 115. Heat is then applied to bond the TCP output pad and pads of the liquid crystal panel through a TAB bonding process. Heat may be applied using a heating tool 130, wherein buffer 132 may be additionally used for uniformly distributing the applied heat. The TCP 101 or 102 may be a part of a flat-TAB or bent-TAB package.
However, since the TCP is heated by the heating tool, heat expansion is generated in the output pad of the TCP. Such heat expansion can cause misalignment between the pads of the liquid crystal panel and the output pad of the TCP. More specifically, as illustrated in FIG. 2B, the gate or data pad 103 or 104 of the liquid crystal panel is rectangular. If the output pad 107 of the TCP is partially distorted by heat expansion, misalignment occurs by varying a contact area of a neighboring pad. Unfortunately, distortions in the output pad of the TCPs not only cause misalignment with the liquid crystal panel in the contact area, but also lead to a non-uniform output voltage to generate image failure.